The implication that comes out of this quote is that Changez believes that the American is assessing and studying him. It is consistent with Changez's initial belief that the American is on some type of mission. This is brought out throughout the narrative. In making clear that he believes the American is observing him and studying him, it furthers the belief that the American is not someone here in an isolated condition. He has been sent to Lahore and is there for a reason, presumably having to do with Changez. In the quote is the idea that there is some level of tension and sense of forboding in the interaction between both Changez and the American. The noticing of the scar on Changez's forearm is a part of this process, something that reflects how both sides in this discussion are not merely speaking to one another, but "sizing" one another up in light of some conflict. The cultural differences between both Changez and the American make a simple gesture like "noticing the scar" on a forearm something more, something adding to the confusion and tension that seems to exist between both men and both sides.